(Not Applicable)
(Not Applicable)
The present invention relates to radio type systems and, more particularly, to improved radiation synthesizer systems enabling efficient use of small high-Q antennas by active control of energy transfer back and forth between an antenna reactance and a storage reactance.
The theory and implementation of Synthesizer Radiating Systems and Methods are described in U.S. Pat. No. 5,402,133 of that title as issued to the present inventor on Mar. 28, 1995. Further aspects are described in U.S. Pat. 6,229,494, titled Radiation Synthesizer Systems and Methods, as issued to the present inventor on May 8, 2001. These patents (xe2x80x9cthe ""133 patentxe2x80x9d and xe2x80x9cthe ""494 patentxe2x80x9d) are hereby incorporated by reference.
A basic radiation synthesizer circuit, as described in the ""133 patent, which combines transfer circuits in both directions using two switches is shown in FIG. 1a. This circuit functions as an active loop antenna where the loop antenna L is the high Q inductive load and a capacitor C is used as the storage reactor. The FIG. 1a circuit uses two RF type switching transistors, shown as switches RC and DC, for rate and direction control, respectively. Because the devices are operated in a switch mode, efficient operation is obtained since, in theory, no instantaneous power is ever dissipated by such devices. A slower switching device, shown as power control switch PC, can be used to add energy to the circuit from the power supply as energy is radiated. The voltage and current sensor terminals VS and CS, respectively, are used to monitor and calculate the total amount of stored energy at any instant in time, while a feedback control circuit is used to maintain the total energy at a preset value through use of the power control switch PC.
In the FIG. 1a circuit, when the direction control switch is open, energy can be transferred from current through the inductor L to voltage across the capacitor C, as illustrated by the L to C energy transfer diagram of FIG. 1b. With the rate control switch closed, current flows from ground, through diode D1 and L, and back to ground through the rate control switch RC. In the absence of circuit losses, the current would continue to flow indefinitely. When the rate control switch RC is opened, the inductor current, which must remain continuous, flows through diode D2 and charges up the capacitor C. The rate at which C charges up is determined by the switch open duty cycle of the switch RC. The capacitor will charge up at the maximum rate when the switch is continuously open. The charging time constant is directly proportional to the switch open duty cycle of the rate control switch RC.
When the direction control switch DC of FIG. 1a is closed, energy can be transferred from voltage across the capacitor to current through the inductor, as shown in the C to L energy transfer diagram of FIG. 1c. Diode D1 is always back biased and is, therefore, out of the circuit. When the rate control switch RC is closed, the capacitor C will discharge through L, gradually building up the current through L. If the rate control switch is opened, the capacitor will maintain its voltage while the inductor current flows in a loop through diode D2. In this C to L direction transfer mode, the rate is controlled by the switch closure duty cycle of switch RC. The maximum rate of energy transfer occurs when the switch RC is continuously closed. Its operation is the inverse of that in the other direction transfer mode (L to C).
It should be noted that, in either direction, charge or discharge is exponential. Therefore, the rate of voltage or current rise is not constant for a given rate control duty cycle. In order to maintain a constant rate of charging (ramp in voltage or current), it is necessary to appropriately modulate the duty cycle as charging progresses. Duty cycle determinations and other aspects of operation and control of radiation synthesizer systems are discussed at length in the ""133 patent (in which FIGS. 1a, 1b and 1c referred to above appear as FIGS. 8a, 8b and 8c).
In theory, since the power which is not radiated is transferred back and forth rather than being dissipated, lossless operation is possible. However, as recognized in the ""133 patent losses are relevant in high frequency switching operations, particularly as a result of the practical presence of ON resistance of switch devices and inherent capacitance associated with switch control terminals. While such device properties are associated with very small losses of stored energy each time a switch is closed, aggregate losses can become significant as high switching frequencies are employed. In addition, if small loop antennas are to be employed, for example, antenna impedance may be higher than basic switching circuit impedance levels, necessitating use of impedance matching circuits which may have less than optimum operating characteristics.
The basic radiation synthesizer circuit discussed above can be reduced to the simplified ideal model shown in FIG. 2. This model replaces the diodes in the basic circuit by ideal switches, and provides push-pull operation (current can flow in either direction through the loop antenna). The push-pull, or bipolar circuit, is more efficient than the single-ended circuit by a factor of 2 (3 dB). The FIG. 2 system includes four power switch devices comprising a switching circuit pursuant to the invention. The FIG. 2 system includes loop antenna 12, storage capacitor 14 and power switch devices 21, 22, 23 and 24, which will also be referred to as switch devices S1, S2, S3 and S4, respectively. Three possible states exist: linear charging of inductor current, linear discharging, and constant current. It is possible to synthesize any waveform using this circuit, with waveform fidelity dependent on sampling speed.
A more complete block diagram of a radiation synthesizer system is shown in FIG. 3. Since each pair of switch devices (i.e., S1/S2 and S3/S4) is always switched in a coordinated manner, and each pair is antiphase, a common control circuit C is used for each pair. Each control circuit C implements sequential switching by delaying the appropriate short circuit transition until after an open circuit transition has been made. This process occurs for each change of state in input driver logic signals provided at the input to control circuit C. Operational and other aspects of the circuits of FIGS. 2 and 3 are described in greater detail in the ""494 patent (in which FIGS. 2 and 3 referred to above appear as FIGS. 2 and 12, respectively).
In addition to applications for signal transmit purposes, it is desirable to apply radiation synthesizer systems to receive applications.
Objects of the invention are, therefore, to provide new and improved radiation synthesizer systems, particularly such as enable one or more of the following advantages and capabilities:
efficient signal reception;
broadband operation;
signal reception using electrically small antennas;
efficient low frequency, small antenna systems;
systems providing signal receive and transmit;
simplified direct synthesis receivers (e.g., no IF processing or detection); and
receivers enabling monolithic circuit construction (e.g., while minimizing number of receiver components).
In accordance with the invention, a radiation synthesizer system, to receive incident signals, includes an antenna element having a first reactive characteristic and a storage element having a second reactive characteristic. At least one switch module is coupled between the antenna element and the storage element and includes switch devices arranged for controlled activation to transfer energy back and forth between the storage element and the antenna element. An output device is coupled to the storage element to enable use of output signals derived, via activation of the switch devices, from signals incident at the antenna element. A control device is coupled to each switch module to control activation of the switch devices in response to indicia of synchronization between activation of the switch devices and the signals incident at the antenna element.
In order to transmit signals as well as receive signals, the control device of the radiation synthesizer system may include a selectable transmit mode in which the control device is responsive to an input signal representative of a signal to be transmitted and is not responsive to the above-referenced indicia of synchronization. For this purpose, the system may further include an input device coupled to the control device to enable coupling of an input signal representative of a signal to be transmitted.
In other embodiments, a radiation synthesizer system may utilize a loop antenna element comprising a plurality of loop segments, with individual switch modules each coupled between a different pair of loop segments. Crossed-loop configurations may be used for isotropic coverage applications and control signal feeds via optical cables and DC feeds via conductors of the loop antenna elements may be employed to provide operational and other advantages in particular applications.
In a further embodiment, a radiation synthesizer, to receive and transmit signals, includes an antenna element having a first reactive characteristic and a storage element having a second reactive characteristic. A switch module is coupled between the antenna element and the storage element and includes switch devices arranged for controlled activation to transfer energy back and forth between the storage element and the antenna element during transmission. A control device is coupled to the switch module to control activation of the switch devices in response to an input signal representative of a signal to be transmitted. An output device is selectively coupled to the antenna element to enable use of output signals received via the antenna element during receive periods in which the switch devices are not subject to controlled activation for energy transfer. Reception is thus enabled by use of the antenna element independently of activation of the switch devices.
For a better understanding of the invention, together with other and further objects, reference is made to the accompanying drawings and the scope of the invention will be pointed out in the accompanying claims.